Support font ligatures

[Tyriar]

Support being removed in #938

It's certainly still possible, the renderer needs to know which characters to join though.

[mofux]

I think we are not interested into the regular ligatures (in fact, it would be bad to enable ligatures for li and such), but for things like ==, !==, => and so on. Here's a nice list of ligatures supported by the fira code monospace font:
https://github.com/tonsky/FiraCode/blob/master/showcases/all_ligatures.png

[LoganDark]

What would happen if half of the ligature is a different color? How would you handle that?

[Tyriar]

@LoganDark does that even work with regular ligatures? Or are they split up when they're different colors?

[LoganDark]

No, and no.

[devsnek]

i wonder if it would be possible to pull render code from txtjs, as they have figured out how to render ligatures, although i think they manually draw the text. http://txtjs.com/examples/Text/ligatures.html

[Tyriar]

@devsnek I don't think it's an issue actually doing the rendering of the text. The issue is knowing which character join so they can be drawn together (Currently "==" is drawn as "=" and "=", not "==").

[devsnek]

@Tyriar wouldn't the font renderer take care of that without our intervention

[Tyriar]

@devsnek yes, but each cell in the grid is drawn individually with a few exceptions (emojis, wide unicode chars). Ligatures need to somehow be included in that list. Look at #938 for more context

[LoganDark]

@devsnek IT'S YOU

disclaimer: completely off topic, just a random comment

[Qix-]

@LoganDark does that even work with regular ligatures? Or are they split up when they're different colors?

If we're going by how other emulators handle them, they do get split up if they are different colors, as one would expect. This is almost a requirement since this allows symbols to be correctly represented by some language highlighters in ViM, for example.

I think it's entirely acceptable to show the individual symbols if the render mode is not the same for all of the underlying characters.